A broadband wireless access (BWA) system provides a point-to-multipoint communication system in a communications network. BWA systems use microwave and millimeter wave technology to transmit communication signals from a wireless base station to a subscriber station located at a fixed site. A BWA system can transmit various types of digital signals including video, voice, television, Internet and other data signals. A BWA system provides easy deployment, minimal environmental impact, and lower infrastructure and real estate requirements. BWA systems are currently being licensed worldwide and in the frequency range from 20 GHz to 42 GHz. The United States government recently completed Local Multi-Point Distribution Service (LMDS) auctions providing 1.3 GHz of bandwidth in the 28 to 31 GHz range nation-wide for BWA systems.
A BWA system is similar to a cellular communication network: both use wireless cells to cover geographic areas, typically from 2 to 5 kilometers in radius. However, whereas in a cellular communication network, a subscriber is mobile and changes location from cell to cell, the subscriber station in a BWA system is located at a fixed site. The transceiver of a BWA subscriber station is at a fixed location and is associated with a particular cell at all times. Also the operating frequency range used by a BWA system is typically much higher than the range used in a cellular communication network.
An important feature of a BWA system is that it bypasses the local loop to the subscriber. A BWA system provides data communications to a subscriber's site over the air without physical cabling to the premises.
Most BWA systems send and receive data using Asynchronous Transfer Mode (ATM), many high quality services can be run concurrently. Thus BWA systems are highly versatile and cost effective for both providers and subscribers of broadband services. In addition to offering traditional services BWA systems can also extend to reach of advanced services such as virtual private networks, encryption, teleconferencing, and voice over IP, distance learning, and telemedicine.
Another feature of a BWA system is that it can be installed quickly. A new BWA system can establish services to a market without existing network infrastructure, such as copper wires or optical fibre, and can rapidly establish a communication network. A BWA system also allows existing providers to complement or expand their existing network to increase or augment their coverage areas.
Another feature of a BWA system is the mobility of its equipment. Unlike a copper wire or optical fibre infrastructure, BWA equipment can be disconnected and transported to another geographic site as required. This is particularly desirable in an industry where there is a high turnover, or churn, rate in customers.
A BWA system has three essential elements: a base station, customer premise equipment and a network management system. A base station is a central location that collects all traffic to and from subscribers within the cell. The base station includes an interface to the wireline or wireless backbone, which is the link between a subscriber and a backbone network. It also consists of a transmitter and receiver, which collects the traffic to and from subscribers within cell.
At a subscriber site, the equipment is similar to equipment at the base station, except that the transmitter, receiver, and antenna are generally housed in a compact unit that is highly directional. The subscribers premise equipment also includes network interface units, which enable a range of communications protocols, such as T1, TOS, the Internet and digital video.
The network management system controls network components and the services being delivered. Ideally the network management system will also provide end-to-end functionality throughout both the wireless and wireline elements of the network.
For signal transmission direction convention, wireless communication signals sent from a base station to subscriber station are sent in a “downstream” direction and wireless communication signals sent from subscriber station to base station are sent in an “upstream” direction.
Communication systems are often modelled in layers. Each layer provides a specific task for the communication systems. Each layer interfaces with its lower and higher layers through standardized protocols. See for example, the OSI layer topology.
The three above elements of a BWA system may be grouped into a physical layer. The services to be provided, such as T1, TOS, Internet, and digital video, may be grouped into an application layer. For effective operation of a communication system, an interface layer is required to properly mesh the services offered by elements in the application layer to the physical equipment in the physical layer. The interface layer may also be modelled as different layers, with interfaces connecting each layer to another layer.
It is desirable to provide a physical layer interface for a wireless communications system that has robustness of implementation and reduced implementation costs.